CD4 and Parkinson disease: The percentage of cTfh cells among CD4+ T cells was significantly higher in PD patients than in HCs [3.68% (2.64–5.70%), 95%CI (3.30, 5.04%) vs. 1.94% (1.32–2.99%), 95%CI (1.61, 2.37%), P < 0.0001, Figure 2B].